Surfactants have become very important chemicals in our society. Many types of surfactants are used for a myriad of applications. Generally, in order to work, surfactants require both water soluble and oil soluble characteristics. It is these mixed characteristics which enable surfactants to lower the interfacial tension between two disparate liquids.
Surfactants have been used in surfactant flooding systems for enhanced oil recovery. However, their use is limited primarily because of the relatively high cost of the surfactants which makes the surfactant flooding systems for oil recovery generally uneconomical. Recently, the economics of surfactant flooding have additionally become even more unfavorable with the low price of oil.
Surfactant flooding to recover oil has been actively investigated due to the relatively poor ability of water floods to displace remaining oil from a reservoir's pore structure. Because of the structure of the reservoir and relative interfacial tensions involved, the flood water may form channels or fingers, bypassing the oil in the formation. Even where water has flowed, residual oil is trapped in pores by viscous and capillary forces. Further flooding with water will not remove such oil.
Investigations of ways to increase oil recovery by improving the displacement ability of water floods have produced useful surfactants which reduce the interfacial tension between oil and water in the reservoir. With lower interfacial tensions, oil that is trapped in the pore structure can be dispersed into the water as smaller and more easily deformable droplets. Many types of surfactants have been investigated and the choice of which surfactant to employ in a water flood operation is dependent upon reservoir characteristics as well as the cost and availability of the surfactants.
Most surfactant floods have employed a petroleum sulfonate as a sole surfactant, or at least a major component of a mixture of surfactants. Synthetic alkyl benzene sulfonates and alkyl sulfonates and sulfates have also been proposed as oil recovery surfactants. To combat separation problems in surfactant mixtures, especially at high salinities (&gt;2% salt), a material with both water soluble and oil soluble characteristics is usually added to sulfonate surfactant mixtures. These materials are generally referred to as "solubilizers" and are usually sulfate or sulfonate salts of polyethoxylated alcohols or alkylphenols. The choice and concentration of solubilizer employed is dependent upon the choice of surfactants used, their overall concentration, and salinity.
Although the reduction of lignin to produce simpler compounds has been extensively studied very few studies have focused on converting lignin to surfactants. The extensive research into the hydrogenation of lignins generally fits into two categories. Studies have been concerned with either the hydrogenation of wood as a pulping method or with the hydrogenation of lignin as a method to produce commodity chemicals. For a more detailed discussion of these studies, see U.S. Pat. No. 4,787,454.
During the last decade, a few studies have focused on converting lignin to surfactants for the purpose of producing economical surfactant flooding systems for oil recovery. These studies have shown that lignin can be converted to water soluble surfactants and used in formulations for enhanced oil recovery chemical floods. The conversion of lignin into surfactants by reduction reactions and their use in chemical flood systems in EOR has been described previously. For instance, U.S. Pat. No. 4,739,040 describes a method of producing surfactants from lignin and is incorporated herein for all purposes. The method consists of reducing the lignin into a complex product mixture called lignin phenols in the presence of a carbon monoxide or hydrogen reducing agent at high temperature and pressure. It was determined that either kraft lignin or lignosulfonates could be reduced by either hydrogen or carbon monoxide in aqueous reactions and yield lignin phenol products. The lignin phenols can then be modified chemically to form water soluble surfactants by one or a combination of several chemical reactions such as alkoxylation, alkylation, sulfonation, sulfation, alkoxylation, and sulfomethylation. The lignin surfactants so produced can be used in surfactant flooding to recover hydrocarbons from underground formations as disclosed in U.S. Pat. No. 4,787,454, which is incorporated herein by reference for all purposes. Other chemical modifications have been developed to further modify the surfactant properties of the lignin phenol surfactants as disclosed in U.S. Pat. Nos. 5,095,985; 5,095,986; 5,230,814; and 5,035,288 and which are incorporated herein by reference for all purposes. For the most part, these chemical reductions have been previously done in aqueous systems. While this reaction system produces suitable products, there are two limitations. First, high pressures are generated because the reaction temperature is usually above the critical point of water (373.degree. C.). Second, the presence of water limits the number of potential catalysts that can be used in the reaction. Because of these limitations, lignin reduction reactions have also been performed in organic solvents and particularly in hydrogen donor type solvents such as tetralin. As a result the reaction pressure is substantially less than the water based reaction. However, effective catalysts needed to be developed because of generally lower yields and poorer surfactant properties in the products.
The literature is replete with references disclosing the liquefaction of lignin with hydrogen in tetralin. Some of these references use various catalysts to promote or alter this reaction. In some of these references, the use of a catalyst in the hydrogenation of lignin in tetralin increased the yield of lignin phenols in the reaction. In addition, many references cite an increase in simple or low molecular weight aromatic products when a catalyst is used.
Schultz et. al. reported on the hydrotreatment of hydrochloric acid lignin in tetralin at about 400.degree. C. Monomeric phenolic products were formed by the cleavage of the ether and the alkyl carbon alpha-beta bonds at a yield of about 11%. Demethylation of the methoxy groups was the dominant reaction occurring under thermal conditions. T. P. Schultz, R. J. Preto, J. L. Pittman, and I. S. Goldstein, J. Wood Chem. and Tech., 1982, 2, 17.
Vuori and Bredenberg reported on the liquefaction of kraft lignin using hydrogen in tetralin as the solvent. The maximum yield of ether soluble phenols and acids was reached when a tetralin/m-cresol mixture was used as the solvent. The main reaction was the demethylation of the methoxyl group leading to the formation of methane. However, high yields of char indicated the inability of both the gas phase hydrogen and the hydrogen from the donor solvent to prevent condensation reactions. Also, the use of a hydro treating catalyst failed to raise the yield of liquid products, instead it increased the amount of gas and char. A. Vuori and J. B. Son Bredenberg, Holzforschuncr, 1988, 42.
U.S. Pat. Nos. 3,105,095 and 3,223,698, assigned to the Noguchi Institute, disclose the catalytic liquefaction of lignin in a hydrogen stream and in a carrier solvent at a temperature of up to 450.degree. C. The catalyst was a composite of iron, tin, copper and sulfur. Disclosed solvents included lignin tar, tetralin, phenols, oil from coal, gas oil, creosote oil and water. The primary object of the Noguchi process was to produce monomeric phenols from lignin to serve as raw materials in organic synthesis. These products are generally unsuitable for surfactants as their equivalent weights are too low.
Train and Klein reported the hydroprocessing of kraft lignin at 380.degree. C. in a hydrogen stream over a composite sulfided cobalt oxide and molybdenum oxide catalyst supported on neutral alumina, having a weight ratio of molybdenum oxide to cobalt oxide of 2:1. The use of a sulfided catalyst composite of molybdenum oxide and nickel oxide supported on neutral alumina, having a weight ratio of molybdenum oxide to cobalt oxide of 5.9:1 in the hydroprocessing of o-hydroxydiphenylmethane was also disclosed. Use of this catalyst induced higher yields of single-ring products and lower yields of light gases compared to hydroprocessing without a catalyst. P. M. Train and M. T. Klein, Fuel Science and Technology, Int'l., 9(2), 193-227, 1991.
Meier et. al. disclosed the catalytic hydropyrolysis of different lignins under different conditions. The use of a composite nickel oxide and molybdenum oxide catalyst supported on zeolite produced oil at a yield of 17% which indicated that the lignin cracking products were unable to get to the active catalyst sites in the zeolite channels. A reaction solvent was not used in these reactions. D. Meier, R. Ante, and O. Faix, Biosource Technology, 1992, 40, 171.
U.S. Pat. No. 4,647,704 disclosed a process for producing monomeric phenols from lignin. The process used a composite of tungsten with a metal on a support. Mildly acidic supports, such as alumina, alumina-silica, aluminum phosphate, and silica-aluminum phosphate were described as being particularly effective. The use of the catalyst increased the yield of phenolic compounds in the hydrocracking of lignin. However, these type of products do not form effective surfactants.
Despite these references, the findings of the present patent disclosure have remained undetected. For instance, the improvement in surfactant properties of the sulfonated lignin phenols observed with the use of the catalyst systems of the present invention is totally unexpected based on the known literature.